1. Field of the Invention
The invention pertains to a process for preparing purified fractions of hemicellulose and cellulose-hemicellulose complexes from alkali treated fiber. Specifically, the process involves the dispersion of alcohol in caustic liquor from alkali treatment of fiber to separate hemicellulose from impurities. The hemicellulose physically separates from the impurities, including cellulose and cellulose-hemicellulose complexes, by floating to the top of the caustic liquor after precipitation with alcohol. Density separation techniques are used to separate the floating precipitated hemicellulose simultaneously, or about simultaneously, with the formation of floating hemicellulose precipitate. The insoluble cellulose and cellulose-hemicellulose complexes can be removed from the caustic liquor by a further separation step.
2. The Prior Art
Fiber consists of hemicellulose, cellulose, some small amount of lignin, oil, starch, and protein. Alkali treatment of fiber, such as corn fiber or other seed fibers, solubilizes about two thirds of the available hemicellulose, and makes an insoluble cellulose-hemicellulose material. Both materials have value as hydrocolloids, however, a complex and difficult separation and refinement has been traditionally necessary to separate the material to produce separate products.
Also, the hemicellulose fraction will have impurities from the alkali separation. Purified hemicellulose has many commercial uses, including uses in the processed food industry; however the value of hemicellulose as a commercial product becomes limited if impurities obtained during the extraction of hemicellulose from fiber remain present in the final hemicellulose product.
U.S. Pat. No. 3,716,526 describes a process for obtaining refined hemicellulose comprising the steps of suspending powdered dried crude hemicellulose in aqueous organic acid and/or organic solvent and then physically separating impurities in the suspension to obtain purified hemicellulose. U.S. Pat. No. 2,868,778 describes a process involving precipitation of hemicellulose from extract by use of a solvent. U.S. Pat. No. 3,935,022 describes a method for treating caustic liquor, such as that originating in the alkaline refining of pulp or viscose manufacture, with one or more organic compounds which have a boiling point below 100° C. and are miscible with water (preferably ethanol) and sodium hydroxide to precipitate hemicellulose from the caustic liquor and then separating the precipitate by ordinary techniques of separation such as filtration, sedimentation and decantation, centrifugation and the like.
We have discovered a process whereby hemicellulose can be separated from caustic liquor by the simultaneous, or about simultaneous, precipitation of the hemicellulose from alkali solutions containing hemicellulose as well as insoluble cellulose and cellulose-hemicellulose complexes, such that hemicellulose precipitate floats on the caustic liquor. Density separation techniques can be used to separate the floating precipitated hemicellulose from the caustic liquor. In the process, the hemicellulose precipitate floats on the top of the caustic liquor as a result of the nature of the alcohol solution used for precipitation and separation parameters. The precipitated hemicellulose is removed from the caustic liquor before it swells and settles into the fluid, mixing with the insoluble cellulose and cellulose-hemicellulose complexes. The cellulose and cellulose-hemicellulose complexes can then be separated from the caustic liquor in a subsequent separation step.
All parts and percentages in this Specification are on a weight-by-weight basis, unless stated otherwise.